Power amplifiers are used in certain communication systems to boost amplitude of a transmitted signal to allow reliable reception by a distant receiver. All power amplifiers exhibit some nonlinear characteristics, and the nonlinear characteristics may be described by quantifying properties of AM/AM and AM/PM curves for the power amplifier. An AM/AM curve represents input amplitude to output amplitude conversion, while the AM/PM curve represents input amplitude to output phase conversion. Nonlinearities caused by the nonlinear characteristics of power amplifiers distort the spectrum of the transmitted signal, causing the bandwidth of the output signal of the power amplifier to be wider than the bandwidth of the input signal of the power amplifier. Consequently, some form of compensation technique is required to produce a power efficient and bandwidth efficient communication system.
One of the compensation techniques used is power amplifier linearization. Power amplifier linearization uses predistortion to distort (e.g., the amplitude, phase or both) the input signal of the power amplifier so that, when combined with the amplifier characteristics, the concatenated input/output characteristic of both the predistortion and the power amplifier is linear. The power amplifier linearization can be either fixed or adaptive. Adaptive power amplifier linearization techniques are the most practical, since these techniques can adapt the predistortion to track changes in the characteristics of the power amplifier due to age, temperature, and other factors.
While there are benefits to adaptive power amplifier linearization, there are also problems associated therewith. It would therefore be desirable to provide techniques that overcome these problems.